1. Field of the Invention
The invention relates to a computer system. More particular, the invention relates to a mother board and a computer system that can flexibly use the synchronous dynamic random access memory (SDRAM) and the double data rate (DDR) DRAM (DDRAM).
2. Description of the Related Art
Currently, a general personal computer comprises a mother board, interface cards and periphery accessories, and the mother board is a heart of the personal computer. On the mother board, in addition to the central processing unit (CPU), the chip set and the slots for installing the interface cards, it further includes the memory module slot to installing memory modules. According to different requirements of users, the amount of the memory module slots for installing memory modules is variable. Typically, a memory module comprises several memory devices.
For the memories normally used in a personal computer such as the synchronous dynamic random access memory, the operation thereof is to perform data access control in correspond with the raising edge of the system clock signal. Under the mode of the double data rate, the memory can perform data access control during both the raising edge and falling edge of the system clock signal. Thus, the operation speed of the memory is fastened.
The difference in operating the SDRAM and the DDRAM includes: (1) the SDRAM uses a normal clock signal, while the DDR DRAM uses a differential clock signal; (2) the VDD of SDRAM equals to 3.3V, the VDD of DDRAM equals to 3.3V, while VDDQ=2.5V; (3) SDRAM does not require a reference voltage, while DDRAM requires a reference voltage; (4) the data bus connected to the SDRAM is normal CMOS logic, and the data bus connected to the DDRAM is series stub terminated logic 2 (SSTLxe2x80x942); (5) the data bus connected to the SDRAM does not require a terminated voltage VTT, but the data bus connected to the DDRAM requires a VTT to absorb reflective electric wave; (6) the data bus connected to the SDRAM does not require using a pull-up resistor, but the data bus connected to the DDRAM requires the pull-up resistor. The advantage of using DDRAM instead of SDRAM is the double data rate.
Currently, the computer using DDRAM belongs to the high cost ones such as net server or advance personal computer. The mother board thereof provides memory module slots for mainly supporting DDRAM. A mother board comprising a chip set memory supporting SDRAM/DDRAM memory modules can also be seen in the market. However, the mother board can only select to support one of the memory modules, for example, either the SDRAM module or the DDRAM module, at a time. Since the data bus connected to the DDRAM module is series stub terminated logic 2, a voltage regulator and several pull up resistors are required on the mother board to provide the terminated voltage VTT for the purpose of absorbing electric wave. Therefore, even the chip set can support both SDRAM/DDRAM modules, only one of them can be selected during production. That is, the mother board to support the SDRAM cannot support the DDRAM. A single mother board cannot support both the SDRAM and the DDRAM. The function of the chip set thus cannot be exploited. While producing the mother board that support DDRAM, the requirement of the voltage regulator and the pull-up resistors are disposed on the mother board. The surface area of the printed circuit board (PCB) is thus increase, the cost is accordingly raised.
The invention provides a mother board that can flexibly uses the SDRAM or DDRAM to enable users to flexibly uses the SDRAM module and the DDRAM module.
A terminated circuit module is also provided in the invention. Thus, the mother board manufacturer can dispose the voltage regulator and the pull-up resistors required by the data bus connected to the DDRAM on the terminated circuit module to save the consumed surface area of the PCB.
Furthermore, a memory module, for example, a memory module with 184 pins, is provided to enable the manufacturer to dispose the SDRAM at a position where a DDRAM is located. In this manner, the SDRAM can also be used for a mother board that comprises a memory module slot supporting a memory with 184 pins.
The mother board provided by the invention comprises several memory module slots, a voltage comparator, a clock generator and a chip set. Each of the memory module slots comprises a reference voltage pin, and the reference voltage pins of the memory module slots are connected to each other in parallel. The voltage comparator is coupled to the reference voltage pins of the memory module slots to detect whether the voltage at the reference voltage pin is equivalent to a reference voltage. The clock generator is coupled to an output of the voltage comparator. When the voltage at the reference voltage pin is equal to the reference voltage, a differential clock signal is generated, and when the votlage is different from the reference voltage, a normal clock signal is generated. The chip set is coupled to the output of the voltage comparator. When the voltage is equal to the reference voltage, the chip set is operated under a double data rate mode. If the voltage is different from the reference voltage, the chip set is operated under a normal data rate mode.
The invention also provides a mother board that comprises;a chip set that supports both SDRAM/DDRAM modules. The voltage regulator and the pull-up resistors required by the data bus connected to the DDRAM module are installed in a terminated circuit module. While the SDRAM module is in use, all the memory module slots have to be inserted with the SDRAM modules. When the DDRAM is selected, the DDRAM modules are installed in the memory module slots, and a memory module subsequent to the DDRAM module is inserted to the terminated circuit module. Thus, one the same mother board, the user can select to use either the SDRAM module or the DDRAM module.
The terminated circuit module of the invention can be applied to a mother board comprising several memory module slots. Each of the memory module slot comprises several signal lines. The terminated circuit module comprises a printed circuit board, a voltage regulator and several terminated resistors. The printed circuit board can be inserted into any of the memory module slots to proved an electrical connection between the terminated circuit module and the memory module slots. The voltage regulator is disposed on the printed circuit board to provide a terminated voltage. The terminated resistors are disposed on the printed circuit board and coupled to the voltage regulator. One side of each terminated resistor is coupled to one of the signal line, while the other side of each terminated resistor is coupled to the terminated voltage. The memory module slots meet the 184 pins or 224 pins of JEDEC standard. The memory module slots comprise reference voltage pins. When the terminate circuit module is inserted into any of the memory module slot, the voltage regulator provides a reference voltage that meets the specification of SSLTxe2x80x942 bus of the JEDEC standard to the reference voltage pin.
The memory module provide in the invention can be applied to a mother board comprising memory module slots. The memory modules comprise a printed circuit board which can be inserted into the memory module slot and several SDRAM modules disposed on the printed circuit board. The memory module meets the specification of the memory module slot with 184 pins or 224 pins of JEDEC standard.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.